Ever repaired a stainless water tank? - SailNet Community

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  #1  
Old 11-27-2009
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Ever repaired a stainless water tank?

I just bought a '79 Alajuela 33 with a leaky stainless fresh water tank.
I've read (D. Casey, N. Calder) that linear poly has many advantages over stainless. I've pulled the old approx. 70-gal. tank, planning to replace it with a couple of molded poly tanks. I still miight.
But now I'm wondering if it's feasable to get the welded seams ground out and re-welded with the correct wire or rod and have a tank that will last another decade or two. I'd get it done by a professional weldor who routinely works with that material.
The SS tank was made to optimize the available space within the keel, and so holds a much bigger water supply. Re-using it will also avoid having to build in supports for a couple rectangular poly tanks. And 2 poly tanks would have 6 potentially leaky fittings between them.
I'd appreciate hearing your experiences or insights.
John V.
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Old 11-27-2009
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Don't know where you're located, but there's a couple of fabricators in the San Diego area that repair SS tanks, so I bet there's someone in your area. Fitted SS tanks are hard to beat when you looking for optimal volume vs space.
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Old 11-27-2009
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Stainless is a perfectly good material for tanks. A good welder should be able to look at the tank and tell you whether it is worth repairing. If you have an air source, you could pressurize the tank on your own and put a soapy liquid on the seams to see pinhole leaks. If there are lots of pinholes, it will be better to replace the tank but if there is only one problem area, it can certainly be ground and rewelded.

My own experience has been that stainless tanks go something like 40 years before needing major work. Tanks under pressure tend to develop pinhole leaks in welds earlier.
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Old 11-27-2009
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I agree, get it welded and maybe you'll get another 30 years out of it.
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Old 11-27-2009
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As long as the SS is in good condition I don't see why you couldn't do what you are proposing but you would need to talk to a fabricator to price out the difference between fixing and making new to see which makes the most sense. Grinding out all the welds and re-doing them is a lot of time/work.
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Old 11-28-2009
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Thanks for the replies. I'll track down a good local stainless steel weldor and have him take a look.
Klem's point is well taken. If one pinhole is leaking, there are others that will eventually start to. Hence my thinking to re-weld all the seams.
Getting the tank out requires removing the plywood sole and cutting up the floor pan, so I want some confidence in the tank.
John V.
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Old 11-28-2009
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Boat water tanks that are made of stainless steel are CRAP and are easily subject to corrosion unless the following (expensive) steps are taken: the internal surfaces must be free of 'weld irregularities' and the wleld should be ground flush and smooth, the internal surface finish (including the weld areas) should be sanded and a high mechanical mirror polish (to ~5 micro inches) followed by 'electropolishing' to get any 'service life' out of tank that receives 'chlorinated' water. ..... all this is entirely too expensive for a boat owner. Boat builders dont do this because its also toooooo expensive to do.

Repair welding that doesnt include the above will result in such a tank immediately subject to 'halide' (from the chlorine in 'city' water) corrosion especially in any 'heat affected zone' from welding etc.

Such tanks can 'easily' and economically be repaired by overlaying the previous welded seams (usually where the leaks will be found) with fiberglass cloth tape, a good strength epoxy and then ....... 'lining' the entire interior surface with a low amine emitting, low 'leachables' epoxy especially formulated for food grade or potable water service. These are FDA rated epoxies for 'potable water service', are applied with a paint roller (just like you apply barrier coat). All you have to do is clean the tank, roughen the internal surface with a grinder/sander, apply the strength epoxy to fill-in the pin holes, apply the cloth and then roll-on the potable rated surface. Most of the boat paint manufacturers offer 'potable water' rated lining epoxies though their 'commerical marine' divisions. A good source for small quantities would be: NSP 120 - NSF 61 Potable water approved Epoxy Adduct (good product, lousy website). You can do most of this work if you have large access ports in the top of the tank or cut new access ports .... can be done in the boat or you can remove the tank and do it in your 'shop'.
You can rebuild most metal tanks (fuel, water, etc.) in this manner at a ***fraction*** of the cost of a new tank.
:-)

Last edited by RichH; 11-28-2009 at 10:31 PM.
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Old 11-28-2009
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RichH-you obviously have more knowledge of the subject than I do. How do you account for so many crappy SS tanks lasting 20-30 years or more, like on my boat? Thanks.
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Old 11-28-2009
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Several reasons .... a 'quality' tank was installed, one that welded up by an 'artist' who did 'full penetration' weld (very difficult in thin metal) without overheating the base metal, didnt have many weld laps, slag, etc. in the weld. The welder may have also passivated the tank when the welding was completed ... most ss tanks for boats arent passivated. The pin holes are usually IN the weld area, especially where the weld is not 'smooth' and the corrosion propagates into the 'irregularities' from substandard welding.

Other may be that you are in an area that has a newer municipal water system that has its source of 'clean' source water with relatively low 'bio-burden' that requires very little chlorine concentration (.25-.5ppm) to keep it 'sanitary' ... instead of some areas that require heavy dosage (1-3+ppm), etc. ... or you may be using 'well water'.
;-)
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Old 11-28-2009
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Reweld the tank. Stainless is an excellent material for water (and fuel) tanks. The water picks up no taste as plastic and fibreglass can, you won't get Alzheimers as with aluminum , and it's very long lasting as jrd and others have said. Every food processing plant, brewery, soft drink plant or dairy is stainless from one end to the other. After all, the tank did last 30 years! Any welder working with stainless can weld it and test it easily. Once welded and pressure tested you should be good for another 30 or so. Does it leak on the bottom? If so it might be from sitting in water.
I will be replacing a leaking molded poly tank with custom stainless just as I have my fuel tank.
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